Loading devices are known in the prior art and used to feed bars to a machine tool. Such machine tools comprise, for example, turning lathes, automatic lathes, turning centers or the like machines for machining bars. EP 0 587 248 A1, for example, shows a loading device for loading bars for machining in a machine tool wherein a bar is first moved from a starting position to an end position and then the bar is fed to the machine tool by starting from the end position in an axial direction. Here, the end position is aligned coaxially with a feeding position in which the bar is to be fed to the machine tool in an axial direction, for example, coaxially with a spindle for receiving the bar to be machined.
FIG. 8A shows a schematic perspective view of the elements relevant for the loading cycle of the loading device of EP 0 587 248 A1, that is, of the relevant elements for the transport of a bar from the starting position to the end position. FIG. 8B shows a schematic side view of the relevant elements for the loading cycle according to the teaching of EP 0 587 248 A1.
The loading device for loading bars for machining in a machine tool according to EP 0 587 248 A1 shows two sliding chutes 16 arranged in parallel in an axial direction of the bar, to which a respective L-shaped holding element 17 is fastened. The sliding chutes 16 are inclined downwardly so that a bar arranged on the sliding chutes 16 rolls down due to its gravity until it is stopped by the holding elements 17 in a holding position. Here, FIG. 8A exemplarily shows a bar 15 in the holding position. This holding position on the sliding chutes 16 corresponds to a starting position of the loading cycle of the loading device. Furthermore, the device comprises two lifting elements 22 also arranged in parallel in an axial direction of the bar, which are used for transporting the bar from the starting position to the end position on the sliding chutes 16. Here, the end position of the bar can be seen by means of the bar 13 in FIG. 8A. For holding a bar in the end position, the loading device of EP 0 587 248 A1 comprises two guiding elements 20 realized semi-circularly in profile and forming an accommodation for a bar 13 on the surface thereof, which bar can be held in the end position. The bar 13 lying in the guiding elements 20 is fed from the end position to the machine tool in an axial direction.
The loading cycle and the transport, respectively, of a bar 13 from the starting position on the sliding chutes 16 to the end position in the guiding elements 20 is schematically shown in FIG. 8B. FIG. 8B shows how a plurality of bars is arranged on the sliding chute and held one behind the other for supply by the holding element 17. The bar 15, which in this case is directly in contact with the holding elements 17, is held in the starting position by the holding elements 17 on the sliding chutes 16. According to the teaching of EP 0 587 248 A1, each of the lifting elements 22 can be moved up and down and is moved to a low position at the beginning of the loading cycle, which is below the bar 15 held in the starting position. Each lifting element 22 comprises a downwardly inclined surface 23 which is joined by a holding portion formed by an upwardly inclined surface 24 at a point 26 that later defines a holding position of the bar in the lifting element 22.
For taking the bar 15 out of the starting position, the lifting elements 22 are vertically moved up until the surfaces 23 come into contact with the bar in the starting position. When the upward movement of the lifting elements 22 is continued, the bar is taken off the sliding chutes 16 in the upward movement out of the starting position and pushed upward along the surface of the upwardly inclined holding elements 17, the bar being supported and pushed upward, respectively, in the upward movement by the surface 23 of the lifting element 22.
The dashed line in FIG. 8B illustrates the position of the lifting elements 22 in a topmost position after the vertical upward movement. Here, the bar 13′ supported by the surface 23 is released from contact with the holding elements 17 and consequently rolls down the downwardly inclined surface 23 of the lifting elements 22 due to its gravity until it abuts the holding area 24 and is then held in the holding position 26, as is shown by the bar having reference numeral 13″.
In a subsequent step, the lifting elements 22 are moved vertically down until the bar is deposited in the round reception portion of the guiding elements 20 in the end position (see the position of the bar in FIG. 8B). Then the bar is fed to the machine tool from this position in an axial direction. The lifting elements 22 move further down vertically and then are ready to transport a next bar from the starting position to the end position in a subsequent upward movement in a further loading cycle.
Although the loading cycle according to EP 0 587 248 A1 provides a simple system for transporting the bar from the starting position to the end position because only one upward movement and one downward movement following thereupon of the lifting element 22 is required to perform the transport from the starting position to the end position. However, the major disadvantage occurs that the bar to be transported, after it has been released from contact with the holding elements 17 in the upward movement of the lifting elements 22, rolls down the downwardly inclined surface 23 due to its gravity and collides with the holding area 24 of the lifting elements 22.
Due to the impact occurring after the roll-down movement of the bar on the surface 23 of the lifting element 22, the major disadvantage results in that the entire loading device coupled to the machine tool is exposed to an impact or a shock which, in addition thereto, is also passed on to the machine tool. Thereby, the machining operations on the machine tool are affected in a negative way. In case of a long-term use of the loading device, it is by all means possible in this case that parts of the loading device or the machine tool will be damaged. Furthermore, such impacts during the loading cycle generate an extremely loud noise when the impact occurs. However, according to FIG. 8B, the further disadvantage results in that the size of the holding area 24 limits the cross-section of the loadable bars because bars having a larger cross-section may be conveyed beyond the holding area 24 after rolling down because of the impulse occurring in the roll-down movement. Furthermore, due to the required roll-down movement of the bar on the surface 23 of the lifting element 22, it is merely possible to transport those bars having a circular cross-section which are suitable for rolling down by means of the device according to the teaching of EP 0 587 248 A1 to the end position. Bars having a cross-section deviating in shape from a circular cross-section, in particular those having an angular cross-section, however, cannot be transported.
With regard to the above-described disadvantages of a loading device according to the teaching of EP 0 587 248 A1, a loading device for loading bars for machining in a machine tool was provided, for example, in EP 1 029 619 A1 which develops a loading device according to EP 0 587 248 A1 such that a low-impact or low-noise loading process during the transport of a bar form the starting position to the end position is accomplished. Here, EP 1 029 619 A1 in particular describes a loading device which also comprises downwardly inclined sliding chutes for supplying bars, wherein a bar disposed on the sliding chutes is held by retaining fingers in a starting position. In this case, the retaining fingers are upwardly inclined.
In analogy to the teaching of EP 0 587 248 A1 the loading device of EP 1 029 619 A1 also comprises a lifting element that can be moved up and down and which receives a bar from the sliding chutes from the starting position and pushes it upward along a surface of the upwardly inclined retaining fingers in analogy to the above-described loading device. However, according to the teaching of EP 1 029 619 A1, in difference to the above-described loading device, a receiving portion of the lifting element is simultaneously used as a holding portion for holding the bar in the end position. Consequently, the moment the bar loses contact with the retaining finger, the bar is received in the receiving portion of the lifting element and then is moved up to the end position only by further moving the lifting element upward, which end position is coaxially aligned with the feeding position in which the bar is axially fed to the machine tool.
In this case, however, the loading device according to the teaching of EP 1 029 619 A1 has the major disadvantage that the device can only be adapted by means of a complicated mechanism to bars of different bar cross-sections. On the one hand, the topmost position must be adapted to the bar cross-section after the upward movement of the lifting element, that is, a bar having a smaller cross-section must be moved to a higher position of the lifting element than a bar having a larger cross-section because it is necessary to coaxially align the center of the bar cross-section in the end position to the feeding position of the machine tool. Additionally, however, it is also required to adapt the angle of inclination and the shape of the retaining fingers, respectively, in dependence of the bar cross-section by means of a complicated mechanism. Here, the topmost position of the lifting element must be adjusted after the upward movement so as to be synchronous with the adapted angle of inclination of the retaining finger.